Railway track circuit apparatus



July 24, 1962 H. DUCKITT ETAL 3,046,390

RAILWAY TRACK CIRCUIT APPARATUS Filed June 8, 1960 INVENTORS fi arwy Duez and lzller' M Sweeenkam n xwz,

Trim Afr P081565) Our invention relates to railway track circuit apparatus. More particularly, our invention relates to direct current track circuit apparatus for railway signaling use in a stretch of track in railway territory where alternating current is employed for the electric propulsion of trains,

and one of the track rails of the stretch is electrically continuous for providing a return path for the propulsion current while the other is divided by insulated joints into track sections defining the limits of the normally energized track circuits employed for railway signaling purposes. Still more particularly, our invention pertains to direct current track circuits, for the track sections in railway territory such as that described, in which full-wave rectifiers supplied with current from an alternating current source provide the direct current for opera-tion of the relays of the track circuits, said relays being normally energized.

In electric propulsion railway territory in which one rail of the track is electrically continuous for the purpose set forth, the flow of propulsion current in the continuous or return rail produces a difference of potential between the points of connection of the rectifier and the track relay to the continuous track rail of a track section, so that alternating propulsion current flows in the track circuit. The track relay is designed to be immune from operation by alternating current and is thus normally unafiected thereby. However, at the end of the track section at which the full-wave rectifier is connected across the rails to provide direct current for operation of the track relay of the track circuit, if the magnitude of the alternating current voltage occurring across the output terminals of the rectifier is sufficiently great, the alternating current intruding into the rectifier will be half-wave rectified and will, therefore, increase the direct current flowing in the track circuit. Such undesirable magnitude of alternating current may especially occur in the event of an interruption of the electrical continuity of the propulsion current return circuit because of a break in the return rail.

It is accordingly the object of our invention to provide apparatus for decreasing to a minimum in electric propulsion railway territory, the possibility of the improper operation of the track relay in a track circuit such as that described, such improper operation resulting from the intrusion of half-wave rectified current into the track circuit because of a substantial increase in the magnitude of the return propulsion current due to a broken return rail, or due to other possible causes of unbalanced conditions of the propulsion current.

Other objects and characteristic features of our invention will become apparent as the description proceeds.

In accomplishing the foregoing object of our invention, we provide means whereby, insofar as possible, the alternating current flowing in the railway signaling track circuit is prevented from intruding into the full-wave rectifier supplying the direct current for said track circuit, and also whereby any alternating current that does so intrude is prevented, insofar as possible, from becoming halfwave rectified and increasing the direct current flowing in the signaling track circuit and overenergizing the track relay.

We shall first describe one embodiment of our invention and shall then point out the novel features thereof in the claim.

atcnt 'icc The accompanying single drawing figure comprises a diagrammatical view showing the apparatus embodying our invention.

Referring to the drawing, there is shown a stretch of railway comprising track rails 11 and 12, the track rail 11 being electrically continuous for the return of the alternating current employed for the propulsion of electric trains to travel the stretch; and the track rail 12 being provided at locations F and G with insulated joints designated 13 and 14, respectively, in the manner well known in the art such that a single rail insulated track section designated A is defined. The railway signaling track circuits provided in such track sections are commonly termed single-rail track circuits since the electrically continuous rail is a common conductor for the track circuits adjacent the track section shown, and also to all such tnack circuits that may be provided adjacent each other in the track stretch.

At'location G the operating coil or winding of a relay 15 is represented in the usual manner by a rectangle and is connected across the rails 11 and 12 at points C and B, respectively; the relay being of the type operated by direct current but immune to operation by alternating current. A normally closed contact 24 is shown in the usual manner below the rectangle representing the relay winding. This contact is employed to control any desired apparatus such as a signal, a switch, a track occupancy indicator, etc., but is indicated in the drawing as controlling a circuit for control or indication apparatus. However, it is to be understood that a contact or contacts of relay 15 may be employed to control any of the apparatus, well known in the art, which is normally controlled by a contact or contacts of the track relay of any normally energized type of railway track circuit.

Adjacent location F there is shown the apparatus, including that of our invention, for supplying direct current energy derived from an alternating current source to the track rails for operation of the track relay of the track circuit. For purposes of simplicity the alternating current source is not shown in the drawing but its terminals are designated BX and NX, respectively. Each of the terminals of the primary winding of transformer 17 are connected to one of the terminals of said current source in the usual manner. The terminals of the secondary winding of the transformer are connected to the input terminals of a full-wave rectifier 19. The positive and negative output terminals of the rectifier are designated by the conventional plus and minus symbols. The positive output terminal of the rectifier is connected through the usual adjustable current limiting resistor 23 and a choke coil 22 to rail 12 of the track section at point B. Similarly, the negative output terminal of the rectifier is connected through a choke coil 21 to rail 11 of the track section at point D. It is readily apparent, therefore, that the direct current output of the rectifier 19 connected across the rails of the track section normally maintains track relay 15 energized and its front contact 24 normally closed. By including a choke coil in each of the circuits connecting the output of the rectifier to the track rails, circuits having a low resistance to direct current but sufliciently high inductance to impede through the rectifier from the negative output terminal to the positive output terminal. Such undesired operation may have the eifect of supplying to the rails of the track section half-wave rectified alternating current, that is, direct current, of sufiicient magnitude to overenergize the track relay thereby decreasing the shunting sensitivity of the track circuit below tolerable limits. In order to prevent, as far as possible, the undesirable efiects described, there is connected across the output terminals of rectifier 19 a shunt path, which, as shown, may comprise a resistor 20. Resistor 20 is preferably of the conventional type comprising a resistive tape wound on a ceramic form, with vitreous enamel filling between the turns. This type of resistor has been found to be inherently less prone to short circuiting or open circuiting of the turns than other practical types. In order to provide protection in the event resistor 20 becomes detached from the rectifier terminals, connections to resistor 20 from the feed circuit, comprising resistor 23, and coils 21 and 22, are made preferably spaced from but close to corresponding connections from the terminals of the rectifier, as schematically indicated in the drawmg.

The value of resistor 20 should be such that it will introduce across the output terminals of rectifier 19 a resistance only sufficiently high, relative to the resistance of the direct current track circuit, that the shunting sensitivity of the track circuit, existing before the addition of the resistor, will not be appreciably affected. By selecting the resistor with such consideration, an effective shunt path for altering propulsion current intruding past the choke coils is provided during the half cycles of such current that rail 12 is positive relative to rail 11. Thus the alternate half cycles of the intruding propulsion current will not appreciably efiect half-wave rectification through the rectifier and'will not, therefore, cause the previously discussed overenergization of the track relay. From this description it is apparent that with apparatus of our invention arranged as shown in the single drawing figure, an arrangement is provided for protection against improper operation of a direct current track circuit fed from a rectified alternating current source, said track circuit being employed in a section of track in alternating current electric propulsion railway territory.

Although we have herein shown and described only one form of apparatus embodying our invention, it should be understood that various changes and modifications may be made therein within the scope of the appended claim without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

In combination, a stretch of railway track having one rail electrically continuous for the return of alternating electric propulsion current and having the other rail provided with insulated rail joints defining first and second ends of a track section, a direct current track relay having its control winding connected across the rails in said track section at said first end, a transformer having a primary and a secondary winding, a source of alternating current connected across the primary winding of said transformer, a full-wave rectifier having its input terminals connected across the secondary winding of said transformer, a first and a second choke coil, a first electrical connection from one output terminal of said rectifier to one of the rails in said track section at said second end and includingin a series circuit said first choke coil and said resistor, a sec ond electrical connection from the other output terminal of said rectifier to the other of the rails in said track section at said second end and including in a series circuit said second choke coil; and a resistor having a value selected so as to provide a high resistance relative to the magnitude of direct current provided at the output terminals of said rectifier and a low impedance relative to a magnitude of alternating current that may intrude from said track rails to the output terminals of the rectifier, said resistor having a first terminal connected to said first electrical connection at a point between said first choke coil and said one output terminal of the rectifier, and a second terminal connected to said second electrical connection at a point between said second choke coil and said other output terminal of the rectifier.

References Cited in the file of this patent UNITED STATES PATENTS 839,365 Corey Dec. 25, 1906 955,402 Howard Apr. 19, 1910 1,177,842 Young Apr. 4, 1916 1,324,912 Lewis Dec. 16, 1919 1,756,589 Gilson Apr. 29, 1930 2,134,962 Warmington Nov. 1, 1938 

